Hi Denzel,
Thank you for your replay.
I cleared W3 Total Caches’s cache. Also I checked with added plugins but there still have this error. I can’t quest which javascript’s text making this error or in the theme or in a child theme as you advised. But, I see that this error element; “Uncaught TypeError: Cannot read property ‘indexOf’ of undefined” indicate to this bellow bold code (“?”) in HTML;

I understood that in this code – (“?”) need to be some information’s code. as this ‘inspects element’ explaining “Uncaught TypeError: Cannot read property ‘indexOf’ of undefined” So I think that there need to be some code in this question mark’s code (“?”).
What do you think? any suggestion?
I’ll appreciate it!